Electrical submersible pumps (ESP) are employed in many oil wells to pump well fluid from the well. A typical ESP has an electrical motor coupled to the pump for driving the pump. A seal section or pressure equalizer connects to the motor for equalizing a pressure of dielectric lubricant inside with the well fluid pressure on the exterior. Usually, the pressure equalizer locates between the motor and pump. The ESP may also have a gas separator connected to a lower end of the pump. A string of production tubing usually supports the ESP within the well. An electrical power cable extends downward alongside the tubing from a well head assembly. A lower portion of the power cable, referred to as a motor lead, extends alongside the pump, gas separator, if employed, and pressure equalizer to a connector at the upper end of the motor.
The motor lead comprises a flat cable with three electrical power wires side by side in a flat configuration. Each electrical power wire includes a copper core or conductor with one or more layers of electrical insulation. A lead sheath may be extruded around the electrical insulation to provide protection in gassy wells. An outer armor band wraps helically around the sub assembly of electrical power wires.
In some wells, the pump can become hot enough to cause damage to the motor lead. Typically, the heat occurs as a result a lack of well fluid flowing through the pump due to gas locking or pump-off conditions. The excess heat in the pump, as well as any excess heat in the pressure equalizer and/or gas separator, may transfer to the motor lead. The excess heat is particularly a problem with motor leads having lead sheaths. Excessive heat causes the lead sheaths to soften and change shape, becoming thinner. If too thin, the lead sheaths may not be able to provide the desired protection to the electrical conductor insulation layers.